Apollo was acquired by Hewlett-Packard in 1989 for US $476 million, and gradually closed down over the period 1990-1997. But after acquiring Apollo Computer in 1989, HP integrated a lot of Apollo technology into their own HP 9000 series of workstations and servers. The Apollo engineering center took over PA-RISC workstation development and Apollo became an HP workstation brand name (HP Apollo 9000) for a while. Apollo also invented the revision control system DSEE (Domain Software Engineering Environment)[1] which inspired IBM Rational ClearCase.[2] DSEE was pronounced "dizzy".

Apollo machines used a proprietary operating system, Aegis, because of the excessive cost of single CPU Unix licenses at the time of system definition. Aegis, like Unix, was based on concepts from the Multics time sharing operating system. It used the concepts of shell programming (ala Stephen Bourne), single level store, and object-oriented design. Aegis was written in a proprietary version of Pascal.

The dual 68000 processor design was to provide automatic page fault switching, with one processor acting as a watchdog, while the other executed the OS and program instructions.[citation needed] When a page fault was raised, the main CPU was halted in mid (memory) cycle while the watchdog CPU would bring the page into memory and then allow the main CPU to continue, unaware of the page fault. Later improvements in the Motorola 68010 processor obviated the need for the dual processor design.

Certain efficiencies were gained by careful design, for example, the memory page size, network packet, and disk sector were all 1K byte in size. With this arrangement a page fault could take place across the network as well as on the individual computer and Aegis file system was a single system of memory mapped files across the entire network. The name space of the network was self discovering as new nodes (workstations) were added.

Domain/OS (Distributed On-line Multi-access Interactive Network/Operating System) was initially a layer over Aegis and was not built on a Unix kernel. Release 10 incorporated large parts of Unix but the burden of backwards compatibility with previous releases led to a system that was larger and significantly slower than the previous ones. In the end, Hewlett Packard shut down the Domain/OS line. Release 10 came out as competitors were gaining ground in the area of graphics and windowing systems, particularly with the trend to open systems and the X Window System.

Another feature was its proprietary token-ring network, which was originally designed to support relatively small networks of, at most, dozens of computers in an office environment. It was a superb design, allowing direct memory access page faulting from any hard drive on the network, but it did not inter-operate with any other existing network hardware or software. The industry widely adopted Ethernet and TCP/IP, a more universal, albeit much slower network. Apollo later added support for these industry standards while continuing to support its own Domain networking using both Ethernet and Token Ring. The Domain networking was modeled after Xerox Network Systems.

The company moved from a proprietary data bus architecture in favor of IBM's AT-bus, as used in the second generation of IBM PCs, and was simultaneously embracing RISC technology moving towards high-end processors, eventually producing the PRISM line.

The company incurred large losses in 1987 in currency speculation due to the trading activities of one individual,[5] and in 1988 from declining demand for its products.[6] In 1989 Apollo was acquired by Hewlett-Packard.[7]